Most pharmacotherapies evaluated in the past for treatment of cocaine dependence have been ineffective. A recent cocaine treatment trial suggested the MAO-B inhibitor selegiline may be use-ful for treatment of cocaine dependence. This experiment is designed to assess the effects of transdermal selegiline on the pharmacokinetics and pharmacodynamics of cocaine and its metabolite benzylecgonine. The effects of cocaine and selegiline on synaptic dopamine will be measured using plasma-concentration time-curves of homovanillic acid (HVA) and prolactin as surrogate markers. The services provided by the GCRC are vital to the successful completion of this study. We will need the GCRC support for the significant outpatient portion of this study. These include clinical admissions procedures, placement of IV catheters, monitoring vital signs shift, recording inputs/outputs, and administration study medication and specialized low-monoamine diet. GCRC staff will also be responsible for the collection, processing, and packaging of study-mandated urine and blood samples, sending urine toxicology screens, and administering several study-related questionnaires at specific times. Performing these functions will aid in obtaining accurate study data and help ensure a safe, stable, and drug-free environment.